This invention relates to the vapor phase sulfonation and neutralization of solid, transparent, resinous polymers to render the surfaces thereof astatic.
It is known from U.S. Pat. No. 2,727,831 that articles of polystyrene can be rendered astatic by liquid phase sulfonation with concentrated sulfuric acid or fuming sulfuric acid followed by treatment with an alkali. It is also known to sulfonate plastics for other reasons as disclosed in U.S. Pat. Nos. 2,400,720, 2,832,698 and 2,937,066 using a variety of sulfonating agents.
This prior art process has various defects in that the sulfonation treatment is slow since the acid has to be drained off the polymer surface for several minutes and then washed with water to remove all traces of the acid. Furthermore, the prior art sulfonation process sometimes renders the polymer yellow or brown and this requires an additional step of bleaching to remove the discoloration. Finally, this prior art sulfonation process has to be run at a relatively high temperature of from about 55.degree. to about 90.degree.C.